Weekend Warrior Q & A

MIG or Stick?

1

I am a welder that welds with a lot of different processes. My question is this. We are welding up a fabrication table to build a container box that will weigh 50,000 lbs. I was told that it should be stick welded with E-7018 and not to weld it with MIG. The MIG wire we use is ER-70.

What is the difference in the two processes? Aren't both electrodes classified as being good for 70,000 psi? Should I make this structural weld with the MIG or Stick?

One of the disadvantages attributed to MIG (GMAW) when performed outdoors is the possible loss of shielding gas due to the wind: this is possibly the concern of those who "told" you to avoid MIG. It depends upon the circumstances, if suitable wind shields can or cannot be set up.

It is accepted that self shielded Flux Cored Arc Welding (FCAW) is less prone to the loss of shielding atmosphere while providing the continuous electrode advantage as MIG does.

As far as strength and stability are concerned the design has to be adequate but there are no differences between the two processes that should bother you as long as sound welds are produced. There may be quite a remarkable difference in the cost of welding though, but this is up for you to decide. However, you are correct in stating that whether you use E-7018 or ER-70 both are rated at 70,000 psi.

Stainless to Mild Steel Welding

Galvanized

3

I was trying to weld a mild steel, galvanized fence post with the stick welding process and I found that my weld would not hold and I had a great deal of pinholes/ globs and the overall weld was horrible. A friend recommended that I try the MIG process instead. Which process should I use to weld a galvanized material?

The stick and MIG process both will not weld galvanized metal. Both of the processes do not allow for the successful expulsion of the vapors created by the zinc coating, thus causing what you describe as “pinholes” and we call porosity. I would recommend you use a gasless process flux cored wire, which has the ability to handle the zinc coating and float it to the surface of the molten weld metal, thus eliminating porosity.

MIG with straight CO2 gas

4

I see a lot of MIG being used, but they are using a straight CO2 gas. In my experience, we always used a CO2/argon mix gas which not only produced a better weld, had less spatter also.

There also were some discussions with my friends who mentioned they will not allow the use of GMAW with only CO2 (carbon dioxide) Gas. Apparently there were some failures resulting from this process.

Is there anything to back this theory up and have you heard anything similar?

The use of CO2 is not forbidden as far as I know, so that failures, if there were any, may be due to other causes too. Gas selection is probably also a question of cost and of ease of supply, especially in developing areas and/or countries.

You are right about spatter and quality, but if Welding Procedure Specifications were approved according to requirements of applicable Codes there is nothing wrong in using straight CO2.

Thickness Range of a Plasma Cutting Machine

5

The capacity of a certain machine is noted as 1 1/2" Manual and 3/4" mechanized. Why would the performance be cut in half when using a machine torch rather than a hand torch?

Plasma machines that can handle both manual and mechanized tasks usually have a lower thickness rating for mechanized cutting rather than manual. This is for several reasons.

Starting and ending the cut on materials close to the maximum thickness properly requires some operator technique that is easy for a human operator but difficult or impossible to program into a machine. Hence a lower rating for satisfactory cuts.

Mechanized cutting requires piercing in most cases rather than edge starts. A machine generally can not pierce successfully as thick as it can cut.

Customers using a machine in an automated set up would generally find the cut speeds on the thickest materials too slow to be acceptable for mechanized operation.

Difference between TIG and MIG

6

What is the difference between TIG and MIG, and what do those letters stand for?

TIG and MIG are 2 very different welding processes. First we will address TIG, Tungsten Inert Gas welding. Advantages of TIG are thin metals as well as thick metals, superior quality, and variety of metals such as aluminum, steel. Disadvantages are that it is more difficult to learn, it is slower in productivity, and it is typically more costly than MIG. Now we will address MIG, which stands for Metal Inert Gas. Some advantages are it is easier to learn (because wire feed is automatic), lower starting costs, faster travel speeds and high productivity.

Warped and Distorted Metal

7

How come when I weld with my small 180 AMP MIG welder on thin material, it often ends up warped and distorted?

The warping or distortion of your base material comes from a build up of heat which in generated by the welding arc and process. To eliminate the warping or distortion, one can weld small sections at a time, thus allowing the heat to not build up and thus eliminating build up so they remain normal (or in their original flat position). For example, if you have a long seem to weld, you could weld starting at the far end, and weld only a couple inches at a time. Then move half way across that area and weld a couple more inches at a time. Then go back to the other area and weld a couple more inches. Repeat this process several times until the entire seem is welded.

MIG (Spitting/ Sputtering/ Excess Spatter)

8

Why is my MIG welding, that I just purchased new, spitting and not welding well?

In most cases the factory settings are designed for flux core welding first and solid wire second. Therefore, the machine is preset at a polarity that is DC -. To correct this problem, change machine to DC + and all will be well. This usually requires looking inside the machine and changing the cable from the DC – to DC +.

MIG: (Burn back to tip)

9

Why is it when I MIG weld I keep getting the wire to burn back up into the tip and then I have to change it?

It could be a couple of things; one being the machine is set for the wrong polarity. However, most typically, you are used to the stick welding process and are moving the gun to close to the plate or your weld puddle. You must make sure you maintain proper arc length which is the distance the nozzle is from the plate. Typically, with a MIG process on mild steel that would be approx ½” - 3/4” of wire protruding from the contact tip.

TIG: Black soot appearing on my weld.

10

When welding aluminum why am I welding smooth and suddenly I get an erratic puddle with black smut (ugly)?

During the welding process you have contaminated the tungsten. You probably did this by either dipping the tungsten into the puddle or when adding filler material the Tungsten absorbed one of your dabs.

MIG Welding: Preheat or not

11

When MIG welding with a 110volt machine should I preheat metal (carbon steel)?¬†

No there is no need to pre-heat at this level of welding. If you are using a 110 MIG machine this means you are welding material that is thin and does not require any pre-heat to have a successful weld.

Preheating without Oxy-Fuel

12

Are there other ways to preheat without using oxy-fuel?

Yes there are other ways to pre-heat. You can also use an oven, and sometimes people will use large heating blankets to keep the weldment hot once it reaches the desired temperature. However, oxy fuel and a torch is the most popular way to pre-heat.

Choosing the correct torch size

13

Torches are usually designed with wp 9, 17, 26. What do these numbers mean?

The numbers represent a type of torch head and the amperage rating. For example: 9 - 125amp aircooled torch, 17 - 150amp aircooled torch, 26 - 200 amp aircooled torch. I prefer the 9 because it is small in size and easy to maneuver. if you are welding production, you will likely want to go watercooled and my favorite is called the 20 style torch which is a 250 amp torch.

The letters "wp" are a manufacturers designation, but all the numbers of the torches are interchangable.

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